This paper discusses the possibility of using the numerical and the physical methods to face the problem of slope stability. A good program to study the distribution of stress and deformation in rock mass is the three-dimensional distinct element code. But at the site, the ground penetrating radar is accurate to detect the circumstance of a mountain body within the limited depth. By comparing results of numerical method and practical method, we can find out several significant features about slope stability.

1. PREFACE

In western China, we are planning to construct many roadways and railways among which the typical difficulty of slope stability is met in mountainous regions. What is studied in this paper is exactly a general slope in mountainous regions. That is the designed route of roadway is along the foot of a hill where the horizontal area is 250m*250m=62500m2. Vertical distance between road surface and vertex of the hill is about 100 meters and inclinations of its five edges are all 60°. The hill is mainly composed of four rock stratas, which, from above to below, are clay, shale, sandstone and limestone, respectively. Their thickness are 10 m, 20 m, 20 m and 50 m. Inclination of each rock mass in the hill is about 30°. Because properties of these five rock masses are different, features of contact plane adjacent to two media must be different. Therefore, which is the main contact plane or the important rock strata to influence the slope stability will be the concern of engineers and technologists.

2. NUMERICAL SIMULATION
2.1 Numerical simulation method

3DEC is a commercial software developed by Itasca Consulting Group, Inc., and is also a program based on the distinct element method, in which a discontinuous medium can be distinguished from a continuous medium by existing interfaces or contacts between the discrete bodies of the system. A numerical model should embody two kinds of mechanical behaviors, which are behavior of discontinuities and behavior of the solid material. It is a special software used in the geotechnical engineering field, especially to simulate slippage of the slope.

2.2 Model construction

Figure 1 illustrates a three-dimensional model about a slope of the hill. Every rock mass in the slope are divided into many stratas by joints whose inclination is strictly 30°.

2.3 Results of numerical simulation

Slope stability can be assessed clearly with respect to stresses, displacement and deformation etc. which are accepted by numerical calculation. Calculations in this paper includes eleven stages, whose time steps are 100, 1000,2000,3000,, 10,000 respectively. Four stages of 100, 1000, 3000 and 5000 time steps are chosen to interpret the development of slope slippage. And in every chosen stage, shear displacement of joints and distribution of principal stresses of rock masses can be directly used to value the effect of rock stratas and contacts to the slope stability (Liu 2000).

2.3.1 Shear displacement

Figure 2 states that displacement of whole system has a tendency to be larger with the increase of time steps.

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